1. Field of the Invention
The present invention relates to a cooling unit for an integrated circuit package.
2. Background Information
Integrated circuits are typically assembled into packages that are soldered to a printed circuit board such as the motherboard of a computer system. The integrated circuit generates heat which must be removed to insure proper operation of the circuits embedded therein. The heat may flow from the package to a heat exchange surface in a conductive process and then removed from the surface by a flow of air generated by a fan of the computer system.
The temperature of the integrated circuit is proportional to the heat generated by the circuits and the thermal impedance between the circuit and the air flow. Newly developed integrated circuits typically generate more heat than their predecessors. It is desirable to provide an electronic assembly which has a lower thermal impedance than the prior art assembly to maintain, or if possible lower, the junction temperatures of the integrated circuit.
The fan requires power to generate the flow of air within the computer system. The power consumed by the fan may reduce the amount of operating time of the computer, particularly for battery power systems such as laptop computers. The fan typically operates at a speed that will remove a maximum amount of heat. The maximum fan speed is not required when the integrated circuit is producing less than maximum heat, for example, when in a power down mode.
There have been developed computer systems that vary the fan speed as a function of the system operating conditions to compensate for variations in the heat generated by the integrated circuit. Varying the fan speed only changes the convective heat transfer rate from the heat exchange surface to the airstream. It would be desirable to vary the conductive heat transfer rate from the package to the heat exchange surface. It would therefore be desirable to provide a cooling unit for an electronic package that can vary the conductive and convective heat transfer rates. It would also be desirable to provide an electronic package assembly that can effectively remove heat from an integrated circuit while minimizing the amount of power consumed by the system.